Highly nonreflective, light absorbing surface coatings and components are well known and used in optical systems. These surface coatings and components absorb light and usually appear very black. Examples of light absorbers include beam stops for low-power lasers, and baffles for eliminating deleterious reflections in telescopes and other optical systems.
In order to be effective in more sensitive optical systems which require high degrees of precision, light absorbers must be materials that are very absorbent, or "black" over the broadest possible range of wavelengths, preferably including infrared.
Conventional light absorbers are typically made from lightweight metals such as beryllium or aluminum and derive their light absorbing properties from a microscopically textured surface developed on the metal by anodization or etching processes. Typical of the anodized material is a composition known in the art as Martin Black 54, a trade name for a proprietary anodized aluminum product developed by Martin Marietta Corporation, Bethesda, Md. Martin Black 54 is one of the best light absorbers, showing excellent absorption and very low scatter throughout a broad range of optical and infrared wavelengths. Unfortunately, the microscopic surface of Martin Black and other anodized light absorber coatings are generally quite fragile. Merely touching the surface with a finger or object can damage the surface and sharply diminish effectiveness as a light absorber.
Etched beryllium light absorbers are somewhat more robust, but have the disadvantage in that they are ineffective above a certain wavelength determined by the physical dimensions of their etched surface features.
Both etching and anodization techniques are critically sensitive to manufacturing process variables, making it difficult to produce components with consistent light absorbing properties, particularly in large size applications. Furthermore, conventional light absorbers made from active metals such as beryllium can be sensitive to moisture or other environmental factors, and those with low melting temperatures have low resistance to thermal and radiation damage.